1. Field of the Invention
This invention relates to a drilling fluid additive system manufactured by a process comprising: admixing colloidal solids such talc with a carrier (such as cellulose or a combination of oil and glycol) to create a suspended mixture to thereby allow the solids to be pre-wet with the carrier; admixing copolymer beads to the suspended mixture to thereby allow the beads to be pre-wet with the carrier and to form a drilling fluid additive mixture; and admixing hydrophilic clay, a pH controller, a fluid loss controller, and a dispersant to the drilling fluid additive mixture. More specifically, the present invention relates to an improved method of enhancing the surface of a cake wall of a well bore by adding a drilling fluid system to the well bore manufactured by the following method: admixing talc with cellulose or a combination of oil and glycol and then admixing polymer beads to the mixture, and subsequently adding this mixture with a mixture of hydrophilic clay, a pH controller, a fluid loss controller, and a dispersant.
2. Description of the Related Art
New technology in drilling for oil and gas now includes horizontal drilling. The horizontal drilling concept exposes more surface area of the producing zone than the conventional vertical drilling operations. For example, if a producing zone is fifty feet in thickness and a vertical well is drilled through such a zone, then only fifty feet of the producing zone will be exposed for production. In contrast, a horizontally drilled well may penetrate the producing sand or zone by one thousand feet or more. The amount or volume of oil or gas production is directly proportional to the horizontal penetration in feet into the producing sand or zone. In horizontal or directional drilling where the drill pipe must bend in order to achieve the desired penetration into the producing zone, friction becomes a major problem. The primary source of friction is directly related to the adhesion of the drilling assembly to the wall cake which lines the drilled well bore. The capillary attractive forces generated by the adhesion of the drilling assembly to the wall cake are directly proportional to the amount or footage of the drilling assembly exposed to the surface of the wall cake.
In horizontal or directional wells, many methods have been used in order to reduce friction between the drilling assembly and the wall cake. One such method would be to add a liquid lubricant to the drilling fluid in order to reduce the coefficient of friction of the drilling fluid. These liquid lubricants include oils, such as hydrocarbon based oils, vegetable oils, glycols, etc. These liquid lubricants will usually reduce the coefficient of friction of the drilling fluid resulting in a reduction of friction between the drilling assembly and the wall cake of the well bore.
When the liquid lubricant is added to the drilling fluid, it has several options as to how it will react. One option is that the lubricant remains isolated and does not mix well with the drilling fluid. A second option is that the lubricant emulsifies with the water in the drilling fluid to form an oil-in-water emulsion. Still another option is the oil attaching itself to the commercial solids in the drilling fluid or to the drilled cuttings or drilled solids. In certain circumstances, some of the liquid lubricant might be deposited or smeared onto the wall cake of the well bore. The ideal scenario would be to have all of the liquid lubricant deposited on the wall cake.
Those experienced in drilling fluid engineering know that a thin, tough, pliable, and lubricious wall cake is most desirable. The integrity of a wall cake is determined by several factors. The thickness of a wall cake is directly proportional to the amount of liquid leaving the drilling fluid, and being forced into the wall of the well bore by hydrostatic pressure. The thickness of the wall cake is also determined by the type and particle size of the solids in the drilling fluid. Particle Size Distribution, or PSD is important to the wall cake integrity. Experts in drilling fluids also know that materials such as bentonite clay, starches, lignites and polymers are all used to build acceptable wall cakes. It is known in the prior art that various food grade vegetable oils are acceptable lubricants when used alone in water-based drilling fluids. It is also known in the prior art that round co-polymer beads when used alone in water-based drilling fluids function as a good friction reducer. However, much more is required to improve the wall cake integrity and lubricity of most well bores. In addition, there is no technology or process in the prior art that improves the lubrication or friction reducing capacity of the copolymer beads.
Furthermore, the solids control equipment used on the drilling rigs today is far superior as to what was used 15 to 20 years ago. In the past, drilling rig shale shakers would probably be limited to screen sizes of about 20-40 mesh on the shakers. These coarser mesh screens would allow pieces of shale and the drilled formation to pass through the shaker screens back into the drilling fluid and then recirculated back down the well bore. As these larger than colloidal size particles make their way back up the well bore to the surface, the action of the drilling assembly rotating within the well bore forces these larger particles into the surface of the well bore. For example: a 20xc3x9720 mesh shaker screen would allow a drilled cutting sized at 863 microns or 0.0340 inches to pass through it and then the cutting would be returned to the well bore and some of these 863 micron cuttings would eventually be embedded into the wall cake. This would give the wall cake surface a texture resembling that of coarse sandpaper. These larger particles would allow the drilling fluid to channel and pass between the drilling assembly and the wall cake thereby reducing the negative effect of the capillary attractive forces generated by the close contact of the drilling assembly with the wall cake. The instances of the drilling assembly becoming stuck to the wall cake when less efficient solids control equipment, such as shale shakers, was used much less than it is today. The more efficient shale shakers today are a great improvement for the drilling fluids but the instances of sticking the drilling assembly are higher. The reason for a higher rate of stuck drilling assemblies today could be blamed on cleaning the drilling fluid to efficiently. Today many drilling rigs utilize cascading shale shakers, which eventually pass the drilling fluid through 200 mesh or 74 micron screens. This is very positive for controlling the percentage of drilled solids in the drilling fluid but it also affects the texture or surface of the wall cake. The finer the solids on the surface of the wall cake are, the greater the capillary attractive forces will be between the drilling assembly and the wall cake.
The present invention provides a method of enhancing the surface of the wall cake. In order to accomplish this, the invention provides a method, which adds something to improve the texture of the surface of the wall cake, and then adds something to prevent large amounts of water from leaving the drilling fluid then passing through the wall cake into the formation. The present invention also provides a carrier for the colloidal solids and beads, which also acts as a lubricant for the drilling fluid. The present invention further provides a process that reduces the effect of capillary attractive forces between the drilling assembly and the wall cake, thereby reducing the tendency of the drilling assembly to become stuck. In high angle directional wells where down hole motors are used to rotate the drill bit and the drill pipe remains stationary, it is important that the drilling assembly can slide as the drilling bit cuts more holes. The present invention improves the ability to slide while drilling as stated above.
In one embodiment, the present invention relates to a drilling fluid additive system manufactured by a method comprising of admixing talc with an oil and a glycol to create a suspended mixture to thereby allow the talc to be pre-wet with the oil and the glycol; admixing copolymer beads to the suspended mixture to thereby allow the beads to be pre-wet with the oil and the glycol and to form a drilling fluid additive mixture, the talc and the beads having an affinity for oils, esters, glycols, cellulose and olefins; and admixing hydrophilic clay, a pH controller, a fluid loss controller, and a dispersant to the drilling fluid additive mixture.
In another embodiment, the beads are comprised of styrene and divinylbenzene. In still another embodiment, the beads have a specific gravity from about 1.0 to about 1.5 and a size from about 40 microns to about 900 microns. In yet another embodiment, the talc has a size range from about 2 microns to about 40 microns.
In still yet another embodiment, the oil and the glycol function as a lubricant. In a further embodiment, the oil consists essentially of oils, hydrocarbon oils, vegetable oils, mineral oils, paraffin oils, synthetic oils, diesel oils, animal oils and soybean oil and mixtures thereof. In still a further embodiment, the glycol consist essentially of polypropylene glycol, polyethoxylated glycol, polybutylene glycol, polyethylene glycol, propylene glycol, polyester polyol-poly(oxyethylene-oxy) propylene glycol, polyoxyalkylene glycol ethers and mixtures thereof.
In yet a further embodiment, the oil and the glycol comprises from about 10% to about 98% of the additive mixture, the talc comprises from about 2% to about 50% of the additive mixture, and the beads comprises from about 2% to about 50% of the additive mixture. In still yet a further embodiment, the system further comprises a weighting agent, said weighting agent consisting essentially of barium sulfate (barite), calcium carbonate, hematite, and salts. In another further embodiment, the system further comprises a surfactant, the surfactant being a nonionic surfactant. In still another further embodiment, the surfactant comprises a polyethoxylated glycol. In still yet another further embodiment, the pH controller consist essentially of caustic acid, potassium hydroxide and sodium hydroxide
In another embodiment, the fluid loss controller consists essentially of lignites, polyacrylamide and graphite uintaite (Gilsonitexe2x80x9d) glycol dispersions. In still another embodiment, the hydrophilic clay consists essentially of bentonite, kaolin clay and viscosifiers. In yet another embodiment, the dispersant consists essentially of lignite and lignosulfonate. In still yet another embodiment, the system further comprises a chemical inhibitor, the chemical inhibitor consisting essentially of gypsum, lime, potassium chloride, potassium hydroxide, magnesium sulfate and calcium sulfate.
In a further embodiment, the method of manufacturing a drilling fluid additive system, the method comprising: shearing colloidal talc with cellulose to create a suspended mixture to thereby allow the talc to be coated with the cellulose and to form a drilling fluid additive mixture; and admixing hydrophilic clay, a pH controller, a fluid loss controller, and a dispersant to the drilling fluid additive mixture. For purposes of this invention, cellulose applies to both the liquid and solid (powder) forms of cellulose and the term coated shall apply to dry and wet coatings and/or treatments of cellulose. In one embodiment, the talc is pre-wet with the liquid cellulose. In another embodiment, the talc is coated with solid (powder) cellulose.
In still a further embodiment, the method further comprises admixing polymeric beads to the drilling fluid additive mixture after coating the talc with the cellulose, the talc and the beads having an affinity for oils, esters, glycols, cellulose and olefins. In yet a further embodiment, the beads have a specific gravity from about 1.0 to about 1.5 and a size from about 40 microns to about 900 microns, the beads comprise of styrene and divinylbenzene.
In still yet a further embodiment, the talc has a size range from about 2 microns to about 40 microns. In another embodiment, the cellulose comprises from about 5% to about 98% of the additive mixture, the talc comprises from about 2% to about 50% of the additive mixture, and the beads comprises from about 2% to about 50% of the additive mixture. In still another embodiment, the pH controller consists essentially of caustic acid, potassium hydroxide and sodium hydroxide. In yet another embodiment, the fluid loss controller consists essentially of lignites, polyacrylamide and graphite uintaite (Gilsonitexe2x80x9d) glycol dispersions. In still yet another embodiment, the hydrophilic clay consists essentially of bentonite, kaolin clay and viscosifiers. In a further embodiment, the dispersant consists essentially of lignite and lignosulfonate.
In still a further embodiment, the method further comprises adding a weighting agent, said weighting agent consisting essentially of barium sulfate (barite), calcium carbonate, hematite, and salts. In yet a further embodiment, the method further comprises adding a surfactant, the surfactant being a nonionic surfactant. In still yet a further embodiment, the method further comprises adding a chemical inhibitor, the chemical inhibitor consisting essentially of gypsum, lime, potassium chloride, potassium hydroxide, magnesium sulfate and calcium sulfate. In another further embodiment, the cellulose consists essentially of polyanionic cellulose, polyanionic cellulose polymer, and carboxymethyl cellulose. In still another further embodiment, the method further comprises adding said system to a wellbore.
In yet another further embodiment, the present invention relates to a method of enhancing the surface of a wall cake of a well bore, the method comprising: shearing colloidal talc with an oil and a glycol to create a suspended mixture to thereby allow the talc to be pre-wet with the oil and the glycol; admixing copolymer beads to the suspended mixture thereby allowing the beads to be pre-wet with the oil and the glycol; adding the suspended mixture to a water-based drilling fluid to form a system, the drilling fluid comprising hydrophilic clay, a pH controller, a fluid loss controller, and a dispersant; and adding the system to a well bore.
In another embodiment, the beads have an affinity for oils, esters, glycols, cellulose and olefins; the beads have a specific gravity from about 1.0 to about 1.5 and a size from about 40 microns to about 900 microns; the beads are comprised of styrene and divinylbenzene. In still another embodiment, the talc has an affinity for oils, esters, glycols, cellulose and olefins; the talc has a size range from about 2 microns to about 10 microns. In yet another embodiment, the oil consists essentially of oils, hydrocarbon oils, vegetable oils, mineral oils, paraffin oils, synthetic oils, diesel oils, animal oils and soybean oil and mixtures thereof.
In a further embodiment, the glycol consists essentially of polypropylene glycol, polyethoxylated glycol, polybutylene glycol, polyethylene glycol, propylene glycol, polyester polyol-poly(oxyethylene-oxy) propylene glycol, polyoxyalkylene glycol ethers and mixtures thereof. In yet a further embodiment, the method further comprises adding a surfactant, said surfactant comprises a polyethoxylated glycol. In still a further embodiment, the method further comprises adding a weighting agent, the weighting agent consisting essentially of barium sulfate (barite), calcium carbonate, hematite, and salts. In still yet a further embodiment, the method further comprises adding a chemical inhibitor, the chemical inhibitor consisting essentially of gypsum, lime, potassium chloride, potassium hydroxide and calcium sulfate.
In another embodiment, the pH controller consists essentially of caustic acid, potassium hydroxide, lime and sodium hydroxide; the fluid loss controller consists essentially of lignites and polyacrylamide; the hydrophilic clay consists essentially of bentonite, kaolin clay and viscosifiers; and the dispersant consists essentially of lignite and lignosulfonate.
In another further embodiment, the talc comprises from about 2% to about 50% of the additive mixture, the oil and the glycol comprises from about 10% to about 98% of the additive mixture, and the beads comprises from about 2% to about 50% of the additive mixture.
In another embodiment, the present invention relates to a water-based drilling fluid additive comprising talc and at least one carrier wherein the carrier may be oils, esters, glycols, cellulose and olefins or combinations thereof. In still another embodiment, the talc is coated or treated with the carrier converting the surface of the talc to a carrier treated or coated surface.